code: def _begin(self):
      if self.cache is None:
          self.cache = ExLlamaCache(self.model)
      else:
          self.cache.current_seq_len = 0
  
file_path: exllama/perplexity.py
imports: from model import ExLlama, ExLlamaCache, ExLlamaConfig
  from tokenizer import ExLlamaTokenizer
  from generator import ExLlamaGenerator
  import json
  import math
  import os
  import sys
  import torch
  import torch.nn.functional
label_desc: Use image node_id 2 for calling the Perplexity obj's underlying member method code with example usage: obj._begin() without return types